The invention disclosed and claimed herein pertains to the field of acoustic signal projection wherein acoustic transducers of different ranges are selectively operated to generate signals across a very wide spectrum. More particularly, the invention pertains to such field wherein a single amplifier is employed to drive all of the transducers in a transducer array. Even more particularly, the invention pertains to such field wherein a crossover network is coupled to a transducer to present a load of comparatively low impedance to the amplifier at frequencies within the operating range of the transducer, and to otherwise present a load of comparatively high impedance.
In order to achieve wide-spectrum acoustic signal projection by means of an array of transducers of comparatively narrow range, means must be provided for selecting a particular transducer to project signals in a particular frequency range. In the prior art, a separate amplifier is coupled to each transducer, and a low level crossover, or steering, network is employed to direct a signal of particular frequency to the amplifier of the transducer capable of generating the particular frequency. However, it has been determined that if the steering network could be eliminated, and if all of the transducers of the array were to be driven by a single amplifier, significant cost and operational advantages could be realized.
In the present invention, a system is provided whereby each transducer in an array of the above type is coupled through a crossover network to a single driving amplifier. The input of a crossover network presents a comparatively low impedance to the amplifier at frequencies within the range of the transducer to which it is coupled, and otherwise presents a comparatively high impedance. The crossover networks are coupled in parallel to a single amplifier. There is no need for the steering network of the prior art, since a transducer is prevented by its crossover network from making more than a negligible response to incoming signals which are not in its frequency range.